A femtocell is a small base station that is deployed in the households or small business environment to get better indoor voice and data coverage, improving at the same time the macrocell reliability. They are a cost-effective solution, able to improve the spectrum efficiency of the network and additionally increase the peak-bit rate in low coverage areas. Femtocells, like macro base stations, may be enabled to communicate to a cellular network by an IP-based backhaul link, which may be a digital subscriber line (DSL) connection or a cable or fiber connection for example.
There are many technical studies and business models elucidating the outstanding potential of femtocells in terms of increasing the network capacity, saving energy and providing benefits from the social and economic side, indicating the femto-based networks as a substantial technological breakthrough on future mobile networks. However, macrocells and femtocells use the same spectrum, originating interference and imposing additional horizontal handover issues that need to be administrated. In addition, the industries are concerned because all the envisaged benefits are not straightforward to achieve, due to major technical and non-technical challenges. In particular, one of the main technical problems comes from the fact that a massive deployment of femtocells will pose serious issues on the radio interference management between the macro and femto layers and among neighboring femtocells.
Conventional solutions like the one described in US 2010/0246482 A1, US 2010/254319 A1 or 2010/0065328 A1 propose the employment of a centralized management entity, which collects radio parameters from the neighboring femtocells and determines and communicates the required transmission configuration for each of them. The main limitation of such methods is the fact that any change in the radio parameters experienced by a single femtocell requires its notification to the centralized management entity and the reconfiguration of the transmission parameters of the plurality of the femtocells. Other solutions like the methods proposed in US/2009 0316649 A1 or US/2010 0111022 A1 are decentralized, i.e. do not require the existence of a centralized management entity, and allow the self-configuration of femtocells when integrated in an existing femtocell network. However, owing to the lack of communication with the neighboring femtocells, these techniques cannot guarantee efficient utilization of the radio resources and, simultaneously, avoidance of performance degradation to the existing femtocell network. In fact these inventions might be affected by the hidden node problem, a well known problem for a person having ordinary skill in the art, since no procedure is envisaged to control the level of the interference generated to the mobile units served by neighboring cells. The method described in US 2010/0054196 A1 however includes the possibility of direct communication among interfering femtocells in order to coordinate antenna radiation patterns and resource allocation parameters in a distributed manner. Nevertheless, the claimed methods again do not guarantee efficient utilization of the available spectrum and, simultaneously, that the aggregate interference level as perceived by any of the femtocell users is kept below a given value. In fact the claimed methods attempt to minimize the aggregate interference using coordinated configuration of transmission parameters but cannot guarantee any specific maximum value. In addition and most importantly, the proposed methods are not well suited to the initial configuration of a femtocell when integrated in an operational femtocell network since they require initiation of a negotiation phase with all neighboring femtocells at start-up.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present disclosure.
The research of the present invention has received funding from the Seventh Framework Programme of the EU [FP7/2007-2011] under grant agreement n° ICT-248 891 STP FREEDOM